1. Technical Field
The invention relates to wheel end assemblies, and in particular to wheel end assemblies for non-drive axles of heavy-duty vehicles, such as tractor-trailers. More particularly, the invention is directed to a wheel hub of a heavy-duty wheel end assembly, in which the wheel hub includes a lubricant fill port that is formed in an existing hubcap bolt hole and which has an internal plug for ensuring containment of the lubricant within the wheel end assembly.
2. Background Art
For many years, the heavy-duty vehicle industry has utilized wheel end assemblies which typically are mounted on each end of one or more non-drive axles. Each wheel end assembly typically includes a hub rotatably mounted on a bearing assembly, which includes an inboard bearing and an outboard bearing, which are in turn immovably mounted on the outboard end of the axle, commonly known as an axle spindle. As is well known to those skilled in the art, for normal operation of the wheel end assembly to occur, the bearing assembly and surrounding components must be lubricated with oil or grease. Therefore, the wheel end assembly must be sealed to prevent leakage of the lubricant, and also to prevent contaminants from entering the assembly, both of which could be detrimental to its performance. More specifically, a hubcap is mounted on an outboard end of the wheel hub, and a main seal is rotatably mounted on an inboard end of the hub and the bearing assembly in abutment with the axle spindle, resulting in a closed or sealed wheel end assembly.
On non-drive axles, such as trailer axles, it is desirable to retain a predetermined amount of lubricant in the wheel end assembly, which increases the life of the bearing assembly, in turn reducing the cost of maintaining and/or replacing the bearing assembly. Historically, oil has been used as the lubricant for the bearing assemblies, but it may not be the optimum lubricant for achieving the goal of increased bearing assembly life. More particularly, if the main seal on the wheel hub assembly degrades, there is a tendency for the oil to leak out of the assembly due to its relatively low viscosity in comparison to other lubricants. When the oil leaks out, the bearing assembly may become under-lubricated, which reduces its life. In addition, in the event of such an oil leak, the main seal usually must be repaired or replaced. Moreover, when the oil leaks out of the wheel end assembly, it may leak onto components of an associated brake system, such as the brake shoes, which must then be repaired, thereby increasing the cost associated with an oil leak. Such potential disadvantages associated with oil leaks have led to increasing use of semi-fluid grease as a replacement for oil as a lubricant for bearing assemblies in wheel end assemblies on non-drive axles.
The higher viscosity of semi-fluid grease causes it to flow less readily than oil, which is an advantage in reducing potential leaks, but creates the need for alternative methods of filling the wheel end assembly with lubricant. That is, with oil, a hole typically is provided in the hubcap, enabling the oil to be poured into the sealed wheel end assembly through the hubcap according to methods that are known in the art. However, semi-fluid grease does not readily flow to both the inboard and outboard bearings and the hub area proximate the bearings using such a hubcap fill hole. Thus, various prior art methods have been developed for filling the wheel end assembly with the proper amount of semi-fluid grease and/or other types of lubricant.
One such prior art method involves mounting only the inboard bearing of the bearing assembly on the axle spindle prior to adding semi-fluid grease to the wheel hub. In the prior art method, the inboard bearing is mounted on the axle spindle, and the wheel hub is mounted on the inboard bearing without the outboard bearing and without a retaining nut, the latter of which typically is used to secure the position of the bearings and the hub on the axle spindle. A nozzle is inserted in the gap between the axle spindle and the hub, and a pre-measured amount of semi-fluid grease is pumped into the gap against the inboard bearing. Once the grease has been added, the outboard bearing is mounted on the axle spindle and the retaining nut is installed and tightened onto the axle spindle.
This method includes a distinct disadvantage, since the lack of the installation of the outer bearing during grease introduction requires that an operator maintain a relatively horizontal position of the wheel hub to prevent damaging the main seal of the wheel end assembly. That is, without the outer bearing in place, there is a tendency for the outboard end of the wheel hub to drop down onto the axle spindle, which in turn can kink or damage the main seal at the inboard end of the wheel hub. In addition, while this prior art method may be employed somewhat efficiently during initial assembly of the wheel end assembly with factory-trained assemblers, it is much less practical for use in the field, such as during servicing of the wheel end assembly, since the wheel end assembly would have to be at least partially disassembled just to add lubricant. As is well-known in the art, it is desirable for lubrication of a wheel end assembly in the field to be performed with minimal disassembly.
Another prior art method involves using a wheel hub that includes a radially-oriented fill port that is formed in the hub wall between the inboard and outboard bearings, and pumping a pre-measured amount of semi-fluid grease into the wheel end assembly through this port. After the lubricant is added, a threaded plug is installed in the port to prevent the lubricant from exiting the wheel hub during service. More particularly, the plug may include a pipe-style interfering thread, or may include a standard thread that compresses an O-ring, which seals the port. This method is preferred over the above-described first prior art method, because the main seal and bearing assembly can be installed with proper alignment before the lubricant is added, so that the main seal typically is not subject to damage during the grease fill operation.
The radially-oriented fill port design is well-known in the art and is relatively simple to manufacture, as long as the wall of the wheel hub has a sufficient thickness to allow an adequate number of threads to be formed to secure the above-described threaded plug in the port. However, when high-strength, thin-wall wheel hub constructions are employed, a radially-oriented fill port formed in the wall of the wheel hub is not practical, since there may not be enough wall thickness in such a wheel hub to form adequate threads to secure a threaded plug. In addition, the formation of the radially-oriented port involves an additional manufacturing operation, which undesirably increases the cost of the wheel hub.
Yet another prior art method of adding lubricant to a wheel end assembly exists, but this method applies only to drive axles, rather than non-drive axles. More specifically, in order to transmit drive torque to a drive wheel, a drive axle and wheel end assembly typically includes a rotating drive shaft that extends through a non-rotating axle spindle. A wheel hub is rotatably mounted on the axle spindle via a bearing assembly, and a set of axially-oriented holes are formed in the outboard end of the wheel hub. The drive shaft is connected at its outboard end to an outboard plate or flange, in which holes are formed that align with the holes in the wheel hub. Drive studs extend through the holes in the plate and into the aligned holes in the wheel hub, where they are seated with an interference fit. In this manner, drive torque from the drive axle is transferred through the plate to the drive studs and to the wheel hub, which rotates about the axle spindle on the bearing assembly for turning the vehicle wheels.
In the prior art lubrication method for such a drive-axle wheel end assembly, one of the holes in the wheel hub, which typically is of a fairly large diameter, such as about ⅝ of an inch, is drilled further inboardly until it breaks into a cavity formed in the wheel hub between the inboard and outboard bearings. Oil-type lubricant then is added into the wheel hub cavity, which enables the lubricant to reach the bearings. Once the proper amount of oil is inserted, the interference-fit drive stud is installed into the wheel hub, and a nut is installed on the outboard end of the stud to secure the connection of the plate to the wheel hub. Once the drive stud is installed in the wheel hub, the stud is not intended to be removed. However, if the drive stud is installed improperly, it may back out during service, in which case centrifugal force could force the lubricant out of the wheel hub, thereby potentially leading to damage of the bearings. More importantly, this method cannot be used on wheel end assemblies for non-drive axles, since such wheel end assemblies lack the structure of drive-axle wheel hubs, and in particular, the outboard plate drive stud assembly, and associated holes formed in the wheel hub. In addition, as described above, this prior art method utilizes oil as the lubricant, rather than semi-fluid grease.
Thus, the above-described disadvantages of prior art methods for properly filling non-drive wheel hubs with semi-fluid grease, as well as the unacceptability of prior art methods employed to fill drive axle wheel hubs due to the differing structure of prior art non-drive axle wheel hubs, makes it desirable to develop a non-drive axle wheel hub that is capable of being filled with semi-fluid grease without manipulation of the outboard bearing or using a radially-oriented fill port, while being economical to manufacture. The present invention satisfies this need.